Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Inputs, Level 1 [Member]
Total Assets	$ 7.8	$ 7.5
Total Liabilities	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	7.8	7.5
Debt Instrument, Fair Value Disclosure		0.0
Total Liabilities	0.0
Fair Value, Inputs, Level 2 [Member]
Total Assets	0.0	0.0
Total Liabilities	1,706.2	1,376.4
Fair Value, Inputs, Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	0.0	0.0
Debt Instrument, Fair Value Disclosure		610.9
Total Liabilities	909.9
Fair Value, Inputs, Level 3 [Member]
Total Assets	0.0	0.0
Total Liabilities	16.8	17.0
Fair Value, Inputs, Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	0.0	0.0
Debt Instrument, Fair Value Disclosure		17.0
Total Liabilities	16.8
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Total Master Trust Assets, Fair Value	0.6	0.5
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.6	0.5
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Mutual Fund | Fair Value, Inputs, Level 1 [Member]
Total Master Trust Assets, Fair Value	7.2	7.0
Mutual Fund | Fair Value, Inputs, Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	7.2	7.0
Mutual Fund | Fair Value, Inputs, Level 2 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Mutual Fund | Fair Value, Inputs, Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Mutual Fund | Fair Value, Inputs, Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Mutual Fund | Fair Value, Inputs, Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Carrying Value [Member] | Debt [Member]
Long-term Debt	1,837.6	1,535.9
Carrying Value [Member] | Debt [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Long-term Debt	1,012.5	712.7
Fair Value [Member]
Total Assets	7.8	7.5
Total Liabilities	1,723.0	1,393.4
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	7.8	7.5
Total Liabilities	926.7
Fair Value [Member] | Money Market Funds [Member]
Total Master Trust Assets, Fair Value	0.6	0.5
Fair Value [Member] | Money Market Funds [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.6	0.5
Fair Value [Member] | Debt [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument, Fair Value Disclosure		627.9
Fair Value [Member] | Mutual Fund
Total Master Trust Assets, Fair Value	7.2	7.0
Fair Value [Member] | Mutual Fund | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	$ 7.2	$ 7.0